Climate | CBSE Class 11 Geography Notes

This note covers weather and climate, regional contrasts, climatic controls, the Indian monsoon, seasonal winds and rainfall, local storms, monsoon branches, traditional seasons, rainfall distribution, agriculture and global warming.

What distinguishes weather from climate in India?

Definition: Weather is the momentary state of the atmosphere, the air surrounding the earth. Climate is the average of weather conditions over a longer period.

Weather can change quickly, perhaps within a day or week. Climate changes imperceptibly, with changes that may be noted after 50 years or even more. A short spell of unusual weather therefore differs from a change in long-term climatic conditions.

Weather elements include temperature, the degree of hotness or coldness; air pressure, the force of air per unit area; and wind direction and velocity. Wind is moving air, and its velocity describes its speed and direction.

Other elements are humidity, the moisture in air, and precipitation, water falling from the atmosphere in forms such as rain or snow. Changes in these elements explain why weather varies between seasons and places.

What gives India a common climatic character?

Monsoon connotes the climate associated with seasonal reversal in wind direction. India has a hot monsoonal climate, also prevalent in south and southeast Asia. Seasonal reversal provides a common rhythm without making every region equally hot, wet or dry.

Kerala and Tamil Nadu differ climatically from Uttar Pradesh and Bihar, yet all have a monsoon type of climate. Regional differences in winds, temperature, rainfall, seasonal rhythm and wetness or dryness form sub-types within this broad monsoonal pattern.

The daily temperature range is the difference between the highest and lowest temperatures in a day. The annual range is the difference between the mean temperatures of the warmest and coldest months. Both help compare coastal and interior conditions.

How large are India's regional contrasts in temperature and rainfall?

Regional diversity appears in both seasonal extremes and conditions on the same day. Temperature is expressed in degrees Celsius (°C). In summer, western Rajasthan occasionally reaches 55°C; in winter, temperatures around Leh can fall as low as minus 45°C.

Case study: How do Churu and Tawang differ?

On a June day, Churu in Rajasthan may record 50°C or more, while Tawang in Arunachal Pradesh hardly reaches 19°C on the same day. This comparison shows how strongly summer conditions can differ within a single monsoonal country.

In Kerala and the Andaman Islands, the day-night difference may be hardly seven or eight degrees Celsius. This contrasts with the much larger daily change possible in the Thar Desert. Seasonal variation and daily variation are distinct ways of comparing temperatures.

Case study: How do Meghalaya and Jaisalmer differ?

Rainfall is measured here in centimetres (cm). Cherrapunji and Mawsynram in Meghalaya's Khasi Hills receive over 1,080 cm annually, while Jaisalmer rarely receives more than 9 cm in the same period. Tura may receive, in one day, rainfall equal to ten years at Jaisalmer.

Timing differs as well. Most parts of India receive rain during June to September. Coastal Tamil Nadu receives rain at the beginning of winter. The Coromandel coast generally remains dry in July and August, while strong rain-bearing storms affect the Ganga delta and Odisha coast almost every third or fifth day in these months.

Which factors determine the climate of India?

India's climate reflects six connected controls: latitude, the Himalayan mountains, distribution of land and water, distance from the sea, altitude and relief. Each affects temperature, winds or rainfall, and their combined influence explains regional contrasts.

How do latitude and the Himalayas matter?

Latitude is angular distance north or south of the equator. The Tropic of Cancer passes east-west through central India. South of it lies the tropical zone, which experiences high temperatures throughout the year with small daily and annual temperature ranges.

Northern India lies in the subtropical and temperate zones, farther from the equator, and experiences high daily and annual ranges. The Himalayas form a climatic divide: they protect the subcontinent from cold northern winds and trap monsoon winds, forcing them to shed moisture within it.

How do water, height and landforms affect climate?

Water heats and cools more slowly than land. Differential heating, or unequal heating of land and sea, creates different seasonal pressure zones. These pressure differences cause the reversal of monsoon winds.

The sea moderates coastal temperatures, producing an equable climate with limited temperature extremes. Mumbai and the Konkan coast experience this influence. Delhi, Kanpur and Amritsar lie farther inland and experience stronger seasonal contrasts.

Altitude means height above sea level. Temperature decreases with height, and thin mountain air makes mountain places cooler than plains. Agra and Darjiling lie on the same latitude, yet their January temperatures are 16°C and 4°C respectively.

Relief means the shape and height of the land surface. It affects temperature, pressure, wind direction, wind speed and rainfall. The windward side faces incoming winds; the leeward side lies away from them.

The windward Western Ghats and Assam receive high rainfall during June to September. The southern plateau remains dry because of its leeward position along the Western Ghats. Location relative to a mountain barrier therefore matters as well as distance from the sea.

How does the southwest monsoon develop and advance?

No single theory has been able to explain the monsoon fully. Differential heating of land and sea is an important part of its explanation, while studying atmospheric conditions over a wider global area helps explain its onset and interruptions.

Definition: The Inter Tropical Convergence Zone (ITCZ) is an equatorial low-pressure zone where trade winds converge and air tends to ascend. Trade winds are winds that approach this zone from the two hemispheres.

How does the seasonal pressure shift change winds?

1. Strong summer heating produces an intense low-pressure area in the northwestern subcontinent. Pressure over the Indian Ocean remains high because water heats slowly.
2. The low-pressure area attracts southeast trade winds across the equator, while the ITCZ shifts northwards.
3. In July, the ITCZ lies around 20°N to 25°N over the Gangetic plain. Here, °N means degrees north latitude. This elongated low-pressure zone is sometimes called the monsoon trough.
4. The southern trade winds cross between 40°E and 60°E. Here, °E means degrees east longitude; longitude measures angular distance east or west of the prime meridian.
5. The Coriolis force, the deflecting effect associated with the earth's rotation, turns these winds so that they blow from southwest to northeast. They become the southwest monsoon.

The ITCZ shift is related to withdrawal of the westerly jet stream from south of the Himalayas. A jet stream is a fast-moving current of air high in the atmosphere; westerly means coming from the west.

An easterly jet stream, coming from the east, sets in along 15°N only after the westerly jet withdraws. This easterly jet is held responsible for the burst of the monsoon, its sudden onset with moisture-laden winds, violent thunder and lightning.

When does the monsoon reach different places?

The southwest monsoon sets in over Kerala by 1 June, reaches Mumbai and Kolkata between 10 and 13 June, and covers the entire subcontinent by mid-July. The first rain substantially reduces temperature. Day temperature declines by 5°C to 8°C between mid-June and mid-July.

Curved lines labelled with dates cross India. The 1 June line reaches the southern tip, June dates extend across the Peninsula, and July dates lie towards the northwest.

See Fig. 4.2 in your NCERT textbook

Photograph: Onset of Monsoon (NCERT Class 11 Figure 4.1). This is a photograph showing a lightning streak in a cloudy sky above trees. It illustrates the stormy setting of onset, rather than a labelled mechanism.

Why do monsoon breaks and variability matter?

A break in the monsoon occurs when rains fail for one or more weeks after several rainy days during the southwest monsoon season. Such dry spells are quite common. Their immediate causes differ between northern India and the west coast.

In northern India, rains are likely to fail when rain-bearing storms are not very frequent along the monsoon trough or ITCZ. On the west coast, dry spells are associated with days when winds blow parallel to the coast.

Note: A monsoon burst is the sudden arrival of rainy winds. A monsoon break is a dry interruption after rain has occurred. Keep the onset event separate from the later dry spell.

How is El Nino connected with variability?

El Nino is a complex weather system involving oceanic and atmospheric conditions and warm currents off Peru in the eastern Pacific. It appears once every three to seven years and brings drought, floods and other weather extremes to different parts of the world.

El Nino affects weather in many places, including India, and is used in forecasting long-range monsoon rainfall. During the strong El Nino event of 1990 to 1991, southwest monsoon onset was delayed over most parts of India by five to twelve days.

Understanding the monsoon requires observations on land, over oceans and in the upper atmosphere. Its variability cannot be described simply by the date of first rain. Onset, dry interruptions and the distribution of rainfall all matter to the seasonal pattern.

What characterises the cold weather season?

Meteorologists recognise four seasons: cold weather, hot weather, southwest monsoon and retreating monsoon. The cold weather season usually begins by mid-November in northern India. December and January are the coldest months in the northern plain.

Mean daily temperature stays below 21°C over most of northern India. Night temperature may be quite low, sometimes falling below freezing in Punjab and Rajasthan. Freezing refers to the temperature at which water turns into ice.

Why is northern India colder than the Peninsula?

Punjab, Haryana and Rajasthan are far from the sea's moderating influence and experience continental climate, with strong temperature contrasts. Himalayan snowfall creates cold-wave conditions. Around February, cold winds from the Caspian Sea and Turkmenistan bring cold waves, frost and fog to northwestern India.

A cold wave is a spell of unusually cold weather; frost is ice deposited on surfaces, while fog consists of tiny water droplets suspended near the ground.

The Peninsula has no well-defined cold weather season. Sea influence and proximity to the equator limit seasonal temperature changes along its coasts. Temperatures in the hills of the Western Ghats remain comparatively low.

What are the pressure and wind conditions?

The northern plain has feeble high pressure; southern India's pressure is slightly lower. Isobars, lines joining places with equal air pressure, of 1019 and 1013 millibars pass through northwest India and the far south respectively. A millibar is a unit of air pressure.

Winds blow from the northwestern high-pressure area towards lower pressure over the Indian Ocean. Their speed is about three to five kilometres per hour. Relief influences direction: winds are westerly or northwesterly along the Ganga Valley and clearly northeasterly over the Bay of Bengal.

Where does winter precipitation occur?

Most of India has no winter rainfall. Land-to-sea winds contain little moisture, and anticyclonic circulation, circulation associated with high pressure, reduces the possibility of rain. However, weak temperate cyclones bring rain to Punjab, Haryana, Delhi and western Uttar Pradesh.

These temperate cyclones, low-pressure weather systems originating over the Mediterranean Sea, travel eastwards across West Asia, Iran, Afghanistan and Pakistan. They gain moisture from the Caspian Sea and Persian Gulf. Their meagre rainfall is highly beneficial for rabi crops, crops grown in the winter season.

Precipitation falls as snow in the lower Himalayas and sustains Himalayan river flow in summer. Average winter rainfall in Delhi is around 53 millimetres, a smaller unit of length than the centimetre. Arunachal Pradesh and Assam receive 25 to 50 millimetres during these months.

How does the hot weather season vary across India?

Temperatures rise in northern India as the sun's apparent position moves northwards in March. April, May and June form the northern summer. The hottest area shifts from the Deccan Plateau towards Gujarat, Madhya Pradesh and then northwestern India.

Southern India's summer is milder than northern India's. In coastal regions, temperature increases towards the interior. Mean daily minimum temperature during summer remains quite high and rarely falls below 26°C.

How do summer pressure and local storms develop?

Excessive heat lowers air pressure over northern India. The northward-moving ITCZ forms a trough roughly from the Thar Desert to Patna and the Chotanagpur plateau. Southwesterly winds arriving by mid-June move conditions towards the rainy season.

The Loo consists of hot, dry, oppressive winds over the northern plains from Punjab to Bihar, with greater intensity between Delhi and Patna. They blow in the afternoon and very often continue well into midnight.

May dust storms are very common in Punjab, Haryana, eastern Rajasthan and Uttar Pradesh. Light rain and cool breezes bring temporary relief. Occasionally, contact between dry and moist air masses, large bodies of air with characteristic temperature and moisture conditions, produces intense local storms with violent winds, torrential rain and even hailstorms.

How do the Arabian Sea and Bay of Bengal branches bring rain?

In early June, strong low pressure over northwestern India attracts southern trade winds. Crossing the equator and passing over warm equatorial currents, they gain abundant moisture. Relief and northwestern low pressure modify their direction as they approach land in two main branches.

Where do the three Arabian Sea branches travel?

1. Western Ghats branch: Winds climb slopes from 900 to 1,200 metres, cool, and give 250 to 400 cm of rain to the windward Sahyadris and Western Coastal Plain. A metre is a unit of length used here for height.
2. Central India branch: Winds strike north of Mumbai and follow the Narmada and Tapi valleys. They bring rain across central India, give the Chotanagpur plateau 15 cm, and join the Bay of Bengal branch in the Ganga plains.
3. Northwestern branch: Winds strike Saurashtra and Kachchh, then cross western Rajasthan along the Aravalis, causing only scanty rainfall. They join the Bay of Bengal branch in Punjab and Haryana; together, the branches bring rain to the western Himalayas.

After crossing the Western Ghats, winds descend, become warmer and lose humidity. They give little rain east of the mountains. This low-rainfall area is called a rain-shadow area, lying on the leeward side of the mountain barrier.

How does the Bay of Bengal branch divide?

The Bay branch strikes Myanmar and southeastern Bangladesh. Myanmar's Arakan Hills deflect a large part towards India, so it enters West Bengal and Bangladesh from the south and southeast. The Himalayas and northwestern thermal low, a low-pressure area produced by heating, then influence its division.

One branch follows the Ganga plains westwards to Punjab. Another moves up the Brahmaputra valley towards the north and northeast. A sub-branch strikes Meghalaya's Garo and Khasi hills. Mawsynram, on the Khasi crest, receives the world's highest average annual rainfall.

The Tamil Nadu coast is parallel to the Bay of Bengal branch and lies in the Arabian Sea branch's rain shadow. These two conditions explain why it remains dry during the southwest monsoon season.

Seven shading classes range from 0 to 20 cm to above 400 cm. The map shows heavy rainfall along the western coastal belt and parts of the northeast, with lower rainfall across the northwest and leeward Peninsula.

See Fig. 4.3 in your NCERT textbook

What happens during the retreating monsoon?

October and November are the retreating monsoon season, when southwest monsoon conditions withdraw. As the sun's apparent position shifts southwards, the Ganga plain's low-pressure trough also moves southwards and the southwest monsoon weakens.

How does withdrawal progress?

1. The monsoon retreats from western Rajasthan by the first week of September.
2. By September's end, it withdraws from Rajasthan, Gujarat, the western Ganga plain and the Central Highlands.
3. By early October, low pressure covers the northern Bay of Bengal; by early November it moves over Karnataka and Tamil Nadu.
4. By mid-December, the low-pressure centre has completely moved away from the Peninsula.

Clear skies and rising temperature occur while the land remains moist. High temperature and humidity make the weather oppressive, a condition called October heat. Temperatures begin falling rapidly in the second half of October, particularly in northern India.

Why does the eastern Peninsula receive rain?

North India is dry during retreat, but October and November are the rainiest months in the eastern Peninsula. Northeast monsoon winds pick up moisture while crossing the Bay of Bengal and bring torrential rain to coastal Tamil Nadu and adjoining southern regions.

Cyclonic depressions, low-pressure storm systems, originate over the Andaman Sea and cross the eastern coast of the southern Peninsula. Tropical cyclones, intense low-pressure storms of tropical regions, are very destructive and particularly affect the densely populated deltas of the Godavari, Krishna and Kaveri.

A few cyclonic storms also strike West Bengal, Bangladesh and Myanmar. A bulk of Coromandel rainfall comes from these depressions and cyclones. Such storms are less frequent in the Arabian Sea.

How are annual rainfall and traditional seasons distributed?

India's average annual rainfall is about 125 cm, with great spatial variation. Spatial variation means differences from place to place. The annual total combines rainfall across the year, whereas seasonal rainfall refers to a particular part of the year.

Which areas receive high, medium, low or inadequate rainfall?

Some parts of the Khasi and Jaintia hills exceed 1,000 cm. The Brahmaputra valley and adjoining hills receive less than 200 cm. Snowfall is restricted to the Himalayan region. These differences underline why a national average cannot describe every locality.

The legend has four classes: more than 200 cm, 100 to 200 cm, 50 to 100 cm and less than 50 cm. Darker shading highlights the western coastal belt and northeastern areas; dotted areas occur in the northwest and parts of the interior Peninsula.

See Fig. 4.4 in your NCERT textbook

How do traditional seasons compare with meteorological seasons?

Indian tradition divides the year into six seasons of two months each. This system reflects practical experience in north and central India. It does not match southern India, where there is little seasonal variation.

How does the monsoon influence economic life?

The agricultural cycle, the yearly sequence of crop-growing activities, revolves around the monsoon. Agriculture depends on southwest monsoon rainfall, making the arrival, amount and distribution of rain central to agricultural prosperity.

Timely and adequately distributed rain is especially important where irrigation, the artificial supply of water to crops, is not developed. Failure of rain adversely affects agriculture in these regions. Rainfall variability brings droughts or floods to some parts of India every year.

What benefits and difficulties result?

Regional climatic differences help farmers grow different types of crops. Except in the Himalayas, temperatures across India remain above the level required for crop or plant growth throughout the year. Winter rain from temperate cyclones is highly beneficial to northern rabi crops.

A sudden monsoon burst creates problems of soil erosion, the removal of soil, over large areas. Thus, the presence of rainfall alone does not ensure agricultural prosperity: its timing and adequate distribution are also important.

Climate also shapes daily life beyond farming. Regional differences appear in food, clothes and house types. These are expressions of climatic diversity within the wider unity of India's monsoon rhythm.

What is global warming and how may it affect climate?

Global warming means an increase in the earth's temperature. Climate has changed in the past at both global and local levels and continues to change imperceptibly. Geological evidence suggests that large parts of the earth were once covered by ice.

How do human activities contribute?

Alongside natural causes, large-scale industrialisation and polluting gases contribute to warming. Human activities release carbon dioxide, particularly through burning fossil fuels. Fossil fuels are fuels formed from ancient organic matter.

Carbon dioxide, methane, chlorofluorocarbons and nitrous oxide are greenhouse gases. The greenhouse effect is warming associated with atmospheric absorption of outgoing long-wave radiation, or heat radiation. These gases contribute to global warming.

Methane, chlorofluorocarbons and nitrous oxide occur in much smaller concentrations than carbon dioxide. They are better absorbers of long-wave radiation and therefore more effective at enhancing the greenhouse effect.

What changes are projected?

The earth's mean annual surface temperature has increased over the past 150 years. It is projected that global temperature will increase by about 2°C by 2100. It is said that warming would melt polar ice caps and mountain glaciers and increase ocean water.

A sea-level prediction gives an average rise of 48 cm by the end of the twenty-first century. This would increase annual flooding. Climatic change would promote insect-borne diseases such as malaria and shift climatic boundaries, making some regions wetter and others drier.

Agricultural patterns would shift, and human populations and ecosystems would experience change. An ecosystem comprises living organisms and their physical surroundings interacting together. These projected consequences connect climatic change with farming, settlements and the wider environment.

Glossary

• Weather — The momentary state of the atmosphere, which can change within a day or week.
• Climate — The average of weather conditions over a longer period, with changes occurring imperceptibly.
• Monsoon — Climate associated with a seasonal reversal in the direction of winds.
• Equable climate — Climate with limited temperature extremes, associated with the moderating influence of the sea.
• Relief — The shape and height of landforms that influence temperature, winds and rainfall distribution.
• ITCZ — The Inter Tropical Convergence Zone, an equatorial low-pressure zone where trade winds meet and air tends to rise.
• Monsoon trough — The elongated low-pressure zone over the Gangetic plain associated with the northward summer shift of the ITCZ.
• Monsoon burst — Sudden onset of moisture-laden monsoon winds, associated with violent thunder and lightning.
• Monsoon break — A dry spell lasting one or more weeks after rainy days during the southwest monsoon season.
• El Nino — A complex oceanic and atmospheric weather system involving warm currents off Peru in the eastern Pacific.
• Loo — Hot, dry, oppressive winds blowing over northern plains from Punjab to Bihar during summer.
• Rain-shadow area — An area receiving little rainfall on the leeward side of a mountain barrier.
• October heat — Oppressive weather produced by high temperature and humidity while the land remains moist during monsoon retreat.
• Greenhouse gases — Atmospheric gases, including carbon dioxide, methane, chlorofluorocarbons and nitrous oxide, that contribute to warming.

Common errors and misconceptions

• Misconception: A common monsoon climate means identical conditions throughout India. Correct: Regional differences occur in temperature, rainfall, winds and seasonal rhythm within the broad monsoonal pattern.
• Misconception: Coastal and interior locations have equally extreme temperatures. Correct: The sea moderates coastal conditions, while places farther inland experience stronger seasonal contrasts.
• Misconception: Monsoon burst and monsoon break describe the same event. Correct: Burst describes sudden onset; a break is a dry spell of one or more weeks after rainy days.
• Misconception: All parts of India receive their main rain in June to September. Correct: Most do, but coastal Tamil Nadu receives rain at the beginning of winter.
• Misconception: There is no winter precipitation anywhere in India. Correct: Temperate cyclones bring rain to northwestern India and snow to the lower Himalayas; other regional exceptions also occur.
• Misconception: Winds give equally heavy rain on both sides of the Western Ghats. Correct: Rising winds bring heavy windward rain, while descending, warming winds give little rain on the leeward side.
• Misconception: India has six meteorological seasons. Correct: Meteorologists recognise four seasons; the traditional calendar used in north and central India has six two-monthly seasons.

Exam-style questions with model answers

Q1. Weather is the momentary atmospheric state and may change within a day or week. Climate is the average of weather over a longer period and changes imperceptibly. Using these facts, distinguish weather from climate in two points. [2 marks]

1. Weather describes the momentary state of the atmosphere and may change within a day or week.
2. Climate describes average weather over a longer period, with changes occurring imperceptibly.

Q2. Water heats and cools more slowly than land, creating seasonal pressure differences; the sea moderates coastal temperatures while inland areas lie farther from this influence; Agra and Darjiling share a latitude but have January temperatures of 16°C and 4°C respectively, with Darjiling at greater height. Explain three climatic controls illustrated by these facts. [3 marks]

1. Differential heating of land and water creates seasonal pressure differences because water warms and cools more slowly than the landmass.
2. Distance from the sea affects temperature contrasts: coastal places experience moderation, while inland areas are farther from this influence.
3. Altitude lowers temperature. The January contrast between Agra at 16°C and Darjiling at 4°C illustrates the effect of greater height at the same latitude.

Q3. Summer heating creates intense low pressure in northwestern India while ocean pressure remains high. The ITCZ shifts northwards. Southeast trades cross the equator between 40°E and 60°E and turn to blow from southwest to northeast because of the Coriolis force. Explain monsoon development in four steps using this information. [4 marks]

1. Strong summer heating establishes an intense low-pressure area over the northwestern part of the Indian subcontinent.
2. Higher pressure over the Indian Ocean creates conditions for winds to move towards the heated landmass.
3. The northward shift of the ITCZ accompanies attraction of southeast trade winds across the equator between 40°E and 60°E.
4. The Coriolis force deflects these winds into a southwest-to-northeast direction, producing the southwest monsoon over the Indian region.

Q4. Arabian Sea winds climb the Western Ghats from 900 to 1,200 metres, cool, and bring 250 to 400 cm of rainfall to the windward Sahyadris and Western Coastal Plain. After crossing, they descend, warm, lose humidity and give little rain to the east. Explain this sequence in five points. [5 marks]

1. The Western Ghats obstruct the moisture-bearing Arabian Sea winds, forcing them to climb mountain slopes from 900 to 1,200 metres.
2. The winds cool as they rise along the slopes, producing the conditions associated with heavy rainfall on the side facing the winds.
3. The windward Sahyadris and Western Coastal Plain consequently receive very heavy rainfall, ranging between 250 and 400 cm.
4. After crossing the Western Ghats, the winds descend and become warmer, which reduces their humidity on the eastern side.
5. These descending winds produce little rainfall east of the mountains, creating the low-rainfall region known as the rain-shadow area.

Q5. The Tamil Nadu coast lies parallel to the Bay of Bengal branch of the southwest monsoon and in the rain shadow of its Arabian Sea branch. During October and November, northeast winds gain moisture over the Bay of Bengal and bring torrential coastal rain. Explain the seasonal contrast in three points. [3 marks]

1. During the southwest monsoon, the Bay of Bengal branch runs parallel to the Tamil Nadu coast, contributing to its dry conditions.
2. The coast also lies in the rain-shadow area of the Arabian Sea branch, reinforcing the limited rainfall of this season.
3. In October and November, northeast monsoon winds cross the Bay of Bengal, gain moisture and bring torrential rain to the coast.

Q6. Most of India lacks winter rain because land-to-sea winds have little humidity and anticyclonic circulation reduces rainfall. Weak Mediterranean temperate cyclones nevertheless bring rain to Punjab, Haryana, Delhi and western Uttar Pradesh, benefiting rabi crops. Their precipitation falls as snow in the lower Himalayas and sustains summer river flow. Explain four points. [4 marks]

1. Most areas lack winter rainfall because winds travelling from land to sea carry little moisture and anticyclonic circulation reduces the possibility of rain.
2. Weak temperate cyclones from the Mediterranean create an exception by bringing rain to Punjab, Haryana, Delhi and western Uttar Pradesh.
3. This rainfall, although meagre, is highly beneficial to the rabi crops grown in northern India during the winter season.
4. Precipitation in the lower Himalayas falls as snow, which sustains water flow in Himalayan rivers during summer.

Q7. India's average annual rainfall is about 125 cm. Rainfall exceeds 200 cm along the west coast, Western Ghats and Meghalaya hills; eastern Tamil Nadu and Bihar receive 100 to 200 cm; Delhi and Haryana receive 50 to 100 cm; Ladakh and most of western Rajasthan receive below 50 cm. Describe the national average and four rainfall categories. [5 marks]

1. The national annual average is about 125 cm, but the supplied regional figures show that this average conceals large differences between places.
2. High-rainfall areas receive more than 200 cm annually and include the west coast, the Western Ghats and the hills of Meghalaya.
3. Medium-rainfall areas receive between 100 and 200 cm annually; eastern Tamil Nadu and Bihar are examples of this rainfall category.
4. Low-rainfall areas receive between 50 and 100 cm annually, with Delhi and Haryana illustrating this lower annual rainfall range.
5. Inadequate-rainfall areas receive below 50 cm annually; Ladakh and most of western Rajasthan belong to this category.

Q8. Agriculture depends on timely, adequately distributed southwest monsoon rain, especially where irrigation is undeveloped. Regional climatic differences allow different crops; variable rain brings droughts or floods; sudden bursts cause soil erosion over large areas; winter temperate-cyclone rain benefits northern rabi crops. Explain five effects of climate on agriculture from this information. [5 marks]

1. Agricultural prosperity depends on timely and adequately distributed monsoon rainfall, with failure particularly damaging in regions where irrigation facilities are not developed.
2. Regional climatic variations support the growing of different types of crops, linking the variety of cultivation to differences in monsoon climate.
3. Rainfall variability brings droughts or floods to some parts of the country, making the distribution of rainfall important to agricultural conditions.
4. A sudden monsoon burst creates problems of soil erosion over large areas, so the arrival of rainfall can also cause difficulties.
5. Winter rain brought by temperate cyclones is highly beneficial for northern rabi crops, giving this smaller seasonal rainfall particular agricultural importance.

Key takeaways

• India has a common monsoonal rhythm, but its regions differ greatly in temperature, rainfall, wind patterns and seasonal timing.
• Latitude, the Himalayas, land and water, distance from the sea, altitude and relief together control India's climate.
• The northward summer shift of the ITCZ accompanies cross-equatorial trade winds that become the southwest monsoon.
• A monsoon burst is sudden onset, whereas a break is a dry interruption lasting one or more weeks after rain.
• The Western Ghats receive heavy windward rainfall, while descending winds create a rain-shadow area on their eastern side.
• The Tamil Nadu coast receives rain at the beginning of winter despite remaining dry during the southwest monsoon season.
• Agricultural prosperity depends strongly on timely, adequately distributed rainfall, especially where irrigation is not developed.
• Greenhouse gases contribute to warming, with projected changes affecting sea level, rainfall patterns, agriculture, human populations and ecosystems.

Test yourself

What are the six main factors controlling India's climate?

They are latitude, the Himalayan mountains, distribution of land and water, distance from the sea, altitude and relief.

What is the ITCZ, and where is it located in July?

The Inter Tropical Convergence Zone is a low-pressure zone where trade winds converge and air tends to rise. In July, it lies around 20°N to 25°N over the Gangetic plain.

Which two main branches bring the southwest monsoon to India?

The southwest monsoon reaches India through the Arabian Sea branch and the Bay of Bengal branch.

Why do the Western Ghats create a rain shadow?

Winds cool and shed heavy rain while rising on the windward slopes. After crossing, they descend, warm, lose humidity and give little rainfall to the east.

How do mango showers and blossom showers differ?

Mango showers help early mango ripening in Kerala and coastal Karnataka. Blossom showers are associated with coffee flowering in Kerala and nearby areas.

What produces October heat?

High temperature and humidity, while the land remains moist during monsoon retreat, produce oppressive weather called October heat.

What are the four meteorological seasons of India?

They are the cold weather season, hot weather season, southwest monsoon season and retreating monsoon season.

Why is winter rain important to northern agriculture?

Although meagre, winter rainfall brought by temperate cyclones is highly beneficial for rabi crops in northern India.